The cyclization of thiosemicarbazide with a-bromoacetophenone can result in the formation of isomeric 1, 3, 4-thiadiazines and two different thiazoles. We studied the use of 4-methyl- and 4-ethylthiosemicarbazide as dinucleophilic building blocks. In this context, we observed an unprecedented rearrangement of a 2-hydrazono-2, 3-dihydrothiazole to a 1, 3, 4- thiadiazine. While ring contractions of 1, 3, 4-thiadiazines to thiazoles are quite common, ...
